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Some background : I live alone and want to totally eliminate the need to run my 40 gallon electric water heater, and since i live in sunny Florida I believe I can do so given my low requirement for hot water. Im going to be building my solar collector very soon when all the materials are gathered. My requirement for hot water usage is to take a relatively quick shower of 5-10 minutes using 100 f. hot water and believe the following plan will handle at least that :

I want to use 3/4"x300' coiled red Pex Tubing which measures 32" diameter x 7" high . I will set this in a box which i will construct out of wooden 2x12's with a 1/2" thick plywood on the backside (treated) for a 36"x36" od Box. . I will lay 4" of dense pink Foamboard in the bottom . A 32" square sheetmetal plate painted with flat high temp. low gloss Black paint (primed first) will be layed on top of the bottom Foamboard . The coiled Pex tubing will be wrapped in heavy duty tin foil sheet to prevent UV light from seeing the Pex , and this foil will be pulled tight around the coil of Pex and also painted high temp flat black. ... then the coil will sit inside the box in direct contact with the sheetmetal plate. A double pane window in frame measuring 36" sq. od (without any inside bars) will be fastened on top of the box for a greenhouse effect. The box will sit against the southside of the house on the ground at a 30 degree angle from vertical in a location where where it will recieve full sun. I will cut the hot water CPVC pipe above the water heater and route to the Solar Panel using 3/4" CPVC (insulated) connecting to the 3/4" Pex tubing stubbed out of the side of the Box using Pex compression fittings . The return CPVC pipe (insulated) will run back to the top of the water heaters hot water supply pipe. (Since my hot water reqirements are very minimal, I opted not to heat the entire water heater) .

Since stagnation temps/pressure in the box are of concern, i plan on securing a section of shiny sheetmetal over the face of the Box for capacity control during the summer months.

Specs on the Pex are 100 psi at 200 f. Specs on the CPVC pipe are 100 psi at 180 f. May aim is to deliver hot water in the 100-120 f. range thru experimenting with how much to cover the front of the Box with the shiny sheetmetal plate .

Total estimated cost for this project is $300 ($100 for the Window , $120 for the coiled Pex, and $80 for the wood and CPVC piping with fittings .

If you have tips, considerations, concerns, etc... I would love to hear them. Thanks. Dave.